JPH0279055A - Electrostatic charge image developing method - Google Patents

Abstract

PURPOSE:To obtain an image of high density and high resolution without inducing any ground fogging by carrying out development by applying a low-frequency AC bias voltage to magnetic toner formed by mixing magnetic toner having the same polarity with magnetic carriers and magnetic toner having the opposite polarity at a specific ratio. CONSTITUTION:The magnetic toner 2 is used which is obtained by mixing 1-20wt.% magnetic toner with the same polarity with the magnetic carriers and 80-99wt.% magnetic toner having the opposite polarity. Then a permanent magnet roll 3 which has N and S magnetic polarities on the surface is provided at the bottom part of a toner tank 1 and a sleeve 4 is provided coaxially with the permanent magnet roll 3; and the both are provided relatively rotatably, a bias voltage source 6 is connected to the sleeve 4, and the low-frequency AC bias voltage is applied to the magnetic toner to perform the development. Consequently, the image of high density and high resolution is obtained without inducing any ground fogging.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for developing an electrostatic image formed on the surface of an image carrier, and particularly to a method using a developer consisting of a magnetic carrier and a magnetic toner. , relates to a method of developing using a magnetic brush method.

[Conventional technology]

When developing an electrostatic charge image formed on the surface of an image carrier, 2
A magnetic brush method is generally used.

The developer used in magnetic brush development is often a two-component developer in which a magnetic carrier and a non-magnetic toner are mixed. On the other hand, there is also a method of using a -component developer consisting of resin and magnetism ↑5) as the developer.

In the former method using a two-component developer.

Although an image with good image density and resolution can be obtained, there is a problem in that the reproducibility of halftones is poor.

On the other hand, in the latter method using a one-component developer,
There are problems such as an increase in the toner charge amount, which causes toner charge a collection and development, and insufficient development due to insufficient toner on the sleeve. As a means to solve these problems, for example,
A developer in which a magnetic carrier and a magnetic toner are mixed as described in the above publication has been proposed, and is said to have the advantages of both the conventional two-component developer and one-component developer. .

[Problems to be Solved by the Invention] In the method for developing an electrostatic image using a developer mixed with a magnetic carrier and a magnetic toner as described above, two-component and one-component developers are used. While this method has various advantages, there is a problem that the image becomes unclear when the coercive force of the magnetic toner is low or when the content of magnetic powder in the magnetic toner is low. In order to solve this problem, it is necessary to increase the amount of triboelectric charge of the +RI toner in order to cause a large amount of magnetic toner to adhere to the electrostatic image in the development area. However, if a large amount of a charge control agent is added to improve the amount of triboelectric charge, for example, there is a problem that the fixing performance decreases.
There is also the problem that magnetic toner adheres to non-image areas, increasing ground blur.

The present invention solves the problems existing in the above-mentioned prior art, and provides an electrostatic image development method that increases the amount of charge of magnetic toner and can obtain images with high density and high resolution without inducing ground blur. The purpose is to provide a method.

[Means to solve the problem] In order to achieve the above object, the present invention has the following features.

An electrostatic charge image is formed on the surface of the image carrier, and a developer consisting of a mixture of a magnetic carrier and a magnetic toner is supplied onto a non-magnetic sleeve which is disposed opposite to the surface of the image carrier and has a magnetic field generating member inside. In the electrostatic charge image developing method of developing the electrostatic charge image by rubbing the surface of the image carrier with a magnetic brush formed on the non-magnetic sleeve, 1 to 20% by weight of a magnetic toner having the same polarity as the magnetic carrier. A magnetic toner prepared by mixing 1 magnetic carrier and 80 to 99% by weight of magnetic toner of opposite polarity is used, and a low frequency alternating current bias voltage is applied to the magnetic toner for development.

A technical method was adopted.

As the magnetic carrier used in the present invention, known carriers can be used, but from the viewpoint of image quality, magnetite and soft ferrite (Ni-Zn type, Mg-Zn type) are preferred.

A carrier containing iron oxide consisting of Cu-Zn type, Ba-Ni-Zn type, etc.) is preferable.

The particle size of the magnetic carrier is 20' to 200 μm (preferably 50 to
150I1m).

In addition, the electrical resistivity of the magnetic carrier is 10~101 because it has an electrode effect! It is desirable to set it to Ω·Cut.

Furthermore, the saturation magnetization of the magnetic carrier is 40 to 70 emu/g.
If it is less than 40 emu/g, carrier will adhere to the image area in the development area, which is not preferable. On the other hand, if it exceeds 70 emu/g, the conveying force becomes excessive and unreasonable force acts on the magnetic toner, which is disadvantageous.

Next, the magnetic toner used in the present invention is formed into a particle size of 5 to 25 βm by mixing magnetic powder, a fixing resin, a charge control agent, a coloring pigment, a dye, a fluidity modifier, a resistance adjuster, etc. However, the content of magnetic powder is preferably 10 to 75% by weight. That is, if the content of the magnetic powder is less than 10% by weight, the saturation magnetization of the magnetic toner will be significantly reduced, and the magnetic toner will easily come off from the sleeve, causing VA magnetic toner scattering, which is disadvantageous. On the other hand, the content of magnetic powder is 75
! If it exceeds II%, fixing performance will deteriorate, which is not preferable.

In order to ensure transferability, the electrical resistivity of the magnetic toner is 10'3 in an electric field of C,4k V/cm.
It is preferable to set it to Ω・1 or more, and the amount of triboelectric charge by the blow-off method of magnetic toner is 5 to 5 in absolute value in order to ensure developability when the magnetic toner has opposite polarity to the magnetic carrier.
It is preferable to set it as 201ic 7g. Frictional charge amount is 5
If it is less than μc/g, the image density will decrease;
Exceeding /g is inconvenient because soil fertility increases.

Next, the fixing resin to be contained in the magnetic toner may be appropriately selected depending on the fixing method (for example, Japanese Patent Laid-Open No. 57-975
(See Publication No. 45). - For example, in the case of a hot roll fixing method, examples include styrene/acrylic copolymer, styrene/butadiene copolymer 5 polyester resin, epoxy resin, and mixed resins thereof.

As the magnetic powder, alloys or compounds containing ferromagnetic elements such as ferrite, mag7tite, iron, cobalt, and nickel can be used, but in order to incorporate them into the toner, the average particle size is 0. A thickness of about 1 to 3 μm is desirable. Since the coercive force of the toner is substantially determined by the coercive force of the magnetic powder, the coercive force of the toner can be adjusted by changing the type of magnetic powder.

The above-mentioned additives include the following. As charge control agents, nigrosine dyes having positive charge characteristics and metal-containing (Cr) azo dyes having negative charge characteristics are generally used. Carbon black is commonly used as a resistance adjuster. Furthermore, hydrophobic silica is often used as a fluidity modifier. The amount of these additions is
If there is too much, the fixing properties of the toner will be affected, so generally 1
It is considered to be less than 9 zero doublets.

The developer used in the present invention is prepared by mixing a carrier and a toner, and the toner mixing ratio (toner concentration) is adjusted to 1.
The content is preferably 0 to 90% by weight. Toner density is 9
When it exceeds 0% by weight, the toner tends to fly away and the amount of spent toner increases.On the other hand, when the toner concentration is less than 10% and 9%, one image becomes less sharp and dust and smearing occur. The toner concentration can be adjusted as appropriate depending on the developing conditions and the like.

The preferred range is 20 to 60% by weight, and the preferred range by weight is 20 to 50% by weight.

In the present invention, the magnetic toner that is charged to the same polarity as the magnetic carrier is contained in an amount of 1 to 20% by weight based on the total magnetic toner. It is added for the purpose of improving the amount of frictional electrification of the magnetic toner. If the content is less than 1% by weight based on the entire magnetic toner, the effect of improving the amount of triboelectric charge is insufficient;
If it exceeds , more magnetic toner will adhere to the non-image area,
This is not preferable as it will cause soil burr.

It is preferable that the developer is conveyed by rotating at least the sleeve in order to prevent magnetic agglomeration of the carrier.

Alternatively, the sleeve and the permanent magnet roll may be rotated in the same direction or in opposite directions.

The development gap is suitably 1.0 m or less in order to ensure a contact width between the magnetic brush and the photoreceptor.

In order for the magnetic brush to come into soft contact with the photoreceptor, it is desirable that the magnetic brush is 0.3 mm or more, and the preferred range is 0.4 to 0.6 tym.
It is. The doctor gap may be set according to the development gap.

In addition, in the present invention, the magnetic properties of the developer are as follows.

Measurements shall be made using a vibrating sample magnetometer (Model VSM-3 manufactured by Toei Kogyo Co., Ltd.) in a magnetic field of maximum 5 kOe.

〔Example〕

The figure is a sectional view of a main part of a developing device according to an embodiment of the present invention. In figure 0, numeral 1 is a toner tank.

Contains magnetic toner 2. A permanent magnet roll 3 having N5VA poles on the surface is provided at the bottom of the toner tank 1, and
A sleeve 4 is provided coaxially with the permanent magnet roll 3, and both are provided so as to be relatively rotatable. The sleeve 4 is made of stainless steel or other non-magnetic material and has a hollow cylindrical shape. Next, 5 is a photoreceptor, which is provided rotatably in the direction of the arrow through the sleeve 4 and the developing gap D. Reference numeral 6 denotes a bias voltage source connected to the sleeve 4, which is applied to prevent magnetic toner charged with the same polarity as the carrier from adhering to the electrostatic charge image and causing ground blur. As the bias voltage, a low frequency AC voltage with a frequency of 2 kHz or less is desirable.

Due to the structure of the base, when the permanent magnet roll 3 and the sleeve 4 are rotated in opposite directions, the magnetic toner 2 contained in the toner tank 1 is stirred by the sleeve 4 through the doctor gap d. The permanent magnet roll 3 is conveyed, and the magnetic poles on the surface of the permanent magnet roll 3 form a magnetic blank, and - the surface of the photoreceptor 5 is rubbed. Therefore, the electrostatic charge image formed on the surface of the photoreceptor 5 can be developed.

Next, a more detailed explanation will be given using a specific experimental example.

Ferrite carrier 60% by weight (Hitachi Metals KBN-100, particle size 7 (1-140 μm) Magnetic toner (A) 28-40% by weight (ρ=lO
"Ω-crIl, TEC=-18ttc/g) Magnetic toner CB) 12 to 0% by weight In this case, the magnetic toner (A) is charged to the opposite polarity to the t11 carrier and contributes to development, while the number d Sex toner (B)
is charged with the same polarity as the magnetic carrier, and the magnetic toner (
This contributes to the improvement of the amount of triboelectrification in A), and the laminate materials and physical properties can be made the same just by changing the polarity of the charge control agent. First, (■sexto1).-(Δ) is prepared as follows.

Sunalene-acrylic co-U (combined 46% by weight (manufactured by Fujikura Kasei Mw -22X 10') magnetite
50% (manufactured by Toda Kogyo EP'F)
500) Polypropylene 3% by weight (Viscol 550P manufactured by Kochu Kasei) Negative charge control agent 1% by weight (Bontron E81 manufactured by Orient Chemical) 20% by weight of the above-mentioned raw materials
After kneading at 0'C and solidifying by cooling.

Pulverized silica (manufactured by Nippon Aerosil [N972)]
0.5 parts by weight of was added and heat treated at l 20'C.

A treatment such as classification was performed to obtain a magnetic toner (A) having a particle size of 5 to 20 μm (7).

Next, a magnetic toner (B) was produced in exactly the same manner as in the magnetic toner (A) except that a positive charge control agent (Bontron N, 01 manufactured by Orient Chemical Co., Ltd.) was used in place of the negative charge control agent.

The magnetic toners (A) and (B) produced as described above were blended in various proportions and mixed with a surface-based ferrite carrier to prepare a developer, and one image evaluation was performed. First, as the photoreceptor 5, an OPC drum (outer diameter 40M) having negatively charged polarity is used.
2 Circumferential speed: 100 cylinders/second (clockwise)), -650
After uniform charging to V.

A semiconductor laser was used to perform divided exposure to form an electrostatic charge image on the back surface. For the developing device, a permanent magnet roll 3 with an outer diameter of 18 mm, 8-pole symmetrical magnetization, and a surface magnetic flux density of 650 G (on the sleeve 4) and a stainless steel sleeve 4 with an outer diameter of 20 mm were used.

Here, set the development gap D = 0.4 mi and the doctor gap d = 0.3 rtrm.

The sleeve 4 was rotated clockwise at 150 r, p, m, and the permanent magnet roll 3 was rotated counterclockwise at 900 r, p, m. Note that sleeve 4 is supplied with direct current as a bias voltage.
600V and AC], k ■(Vr-p, f=80
0 Hz) was applied. Corona transfer device after development (+4.
5) and transferred to plain paper using a heat roll coated with PFA resin and a silicone rubber roll.

Fixing pressure 1.0 kg/crs, fixing temperature 180'
It was established under the conditions of C. The table shows the results of image evaluation based on image density, resolution, and soil blur. In addition.

The relative contents of magnetic toners (A) and (B) in the table are (
).

As is clear from the table, in No. 1, reservoir fog occurs due to a large amount of magnetic toner (B) that is charged with a polarity opposite to the normal charging polarity. This is the result of the magnetic toner, which is charged to the opposite polarity, being attached to the non-image area. On the other hand, No,
In No. 5, since the magnetic toner (B) was not present at all, the amount of charge was insufficient and the density of one image was low. No to this
, in 2-4.

Since it contains an appropriate amount of magnetic l·ner (B) that is charged with opposite polarity, it is possible to obtain high-density images without causing blurring.

[Effects of the Invention] Since the electrostatic charge image developing method of the present invention has the structure and operation as described above, it is possible to increase the amount of charge of the magnetic toner, and to produce high-density and high-density images without inducing soil blurring. This has the effect that an image with high resolution can be obtained.

[Brief explanation of the drawing]

The figure is a sectional view of essential parts showing a developing device in an embodiment of the present invention. 3: Permanent magnet roll, 4 sleeves.

Claims (3)

[Claims] (1) Development in which an electrostatic charge image is formed on the surface of an image carrier, and a magnetic carrier and magnetic toner are mixed on a non-magnetic sleeve that is disposed opposite to the surface of the image carrier and has a magnetic field generating member inside. In the electrostatic charge image developing method, the electrostatic charge image is developed by supplying an agent and rubbing the surface of the image carrier with a magnetic brush formed on the non-magnetic sleeve. 20% by weight, and 80-99% by weight of magnetic toner with opposite polarity to the magnetic carrier.
1. A method for developing an electrostatic image, comprising using a magnetic toner prepared by mixing the above, and developing the magnetic toner by applying a low frequency alternating current bias voltage to the magnetic toner. (2) The electrostatic image developing method according to claim (1), wherein the magnetic carrier is formed of ferrite powder. (3) Claim in which the AC bias voltage is 2kHz or less (
The electrostatic image developing method described in 1) or (2).